_South America._—The Greater Antilles were larger than at present and Cuba was much extended, especially to the southeastward, and was probably connected with the mainland, not as one would naturally expect, with Yucatan, but with Central America; this island, it is most likely, was cut off from Hayti. The Isthmian region was considerably broader than it is now and afforded a more convenient highway of intermigration. Costa Rica was invaded by a Pliocene gulf, but it is not yet clear whether this persisted for the whole or only a part of the epoch. In the Argentine province of Entrerios is a formation, the _Paraná_, which is most probably Pliocene, though it may be upper Miocene. This formation is largely marine and shows that the present Rio de la Plata was then a gulf from the Atlantic. A few northern hemisphere mammals in the Paraná beds show that the migration had advanced far into South America. A large part of Patagonia was again submerged beneath the sea, which extended to the Andes in places, but just how general the submergence was, it is impossible to say, for the _Cape Fairweather_ formation has been largely carried away by erosion and only fragments of it remain. Along the foothills of the Andes these beds are upturned and raised several thousand feet above the sea-level, a proof that the final upheaval of the southern mountains took place at some time later than the early Pliocene. Continental formations of Pliocene date are largely developed in Argentina; the _Araucanian_ stage is in two substages, one in the province of Catamarca, where the beds are much indurated and were involved in the Andean uplift, the other, of unconsolidated materials, is at Monte Hermoso near Bahia Blanca on the Atlantic coast. The very small proportion of northern animals in the Araucanian beds is surprising, but not more so than the almost complete absence of South American types in the upper Miocene and lower Pliocene of the United States. Intermigration between the two Americas would seem to have been a much slower and more difficult process than between North America and the Old World, and the reason for the difference is probably the greater climatic barriers involved in a migration along the lines of longitude. Upper Pliocene is found in the Tarija Valley of Bolivia and probably also in Ecuador, in both of which areas the proportion of northern animals was very greatly increased. II. QUATERNARY PERIOD The Quaternary period was a time of remarkable geographical and climatic changes, which had the profoundest and most far-reaching effects, partly by migration and partly by extinction, upon the distribution of animals and plants, effects which are naturally more obvious than those of earlier geological events, just because they were the latest. It is customary to divide the period into two epochs, (1) the _Pleistocene_ or _Glacial_, and (2) the _Recent_, which continues to the present day. 1. _Pleistocene Epoch_